1. Field of the Invention
The present invention generally relates to a semiconductor LED (light emitting diode) device, and, in particular, to an AlGaInN-based LED device which may produce multi-lights with different wavelengths and therefore emit white light by mixing those lights.
2. Description of the Background Art
Generally, switching devices such as a metal semiconductor field effect transistor and a high electron mobility transistor HEMT, and light devices such as a semiconductor laser or a light emitting diode, are used as compound semiconductor devices.
A semiconductor laser has a smaller driving current and size than those of other lasers. The semiconductor laser can directly transform the intensity and frequency of light according to variation of current. The semiconductor laser has some advantages in that it usually has high efficiency of more than 70%, and has a wide wavelength range. As a result, the semiconductor laser is widely used as optical communication appliances, office appliances such as a laser printer or a bar-code reader, and other small-sized appliances.
FIG. 1 is a cross-sectional view illustrating a first example of the conventional LED device, wherein an insulating substrate, which is transparent, is used.
A buffer layer 11, an n-type AlGaInN layer 12, an AlGaInN active layer 13, a p-type AlGaInN layer 14 and a transparent electrode 15 are sequentially stacked on an insulating substrate 10. A p-type metal electrode 16 is formed on one side of the transparent electrode 15.
An n-type metal electrode 17 is formed on the exposed portion of the n-type AlGaInN layer 12. This exposed portion is made by removing portions of the p-type AlGaInN layer 14, the active layer 13, and the n-type AlGaInN layer 12 on the other side of the substrate 10. Thus light may be emitted into the upper and lower sides of the insulating substrate 10.
FIG. 2 is a cross-sectional view illustrating a second example of the conventional LED device, wherein a conductive semiconductor substrate is used.
A buffer layer 21, an n-type AlGaInN layer 22, an AlGaInN active layer 23 and a p-type AlGaInN layer 24 are sequentially stacked on one side of a conductive semiconductor substrate 20 such as Si or SiC. A p-type metal electrode 26 is formed on the upper surface of the p-type AlGaInN layer 24. An n-type metal electrode 27 is formed beneath the lower surface of the conductive semiconductor substrate 20.
As described above, in general, compound semiconductor light emitting devices have structures in which holes from the p-type metal electrode combine with electrons from the n-type metal electrode in a single/multi-layered active layer to emit light corresponding to the bandgap of material composition of the active layer. Most of the light is emitted from the p-n junction type active layer to the upper and lower surfaces of the active layer.
Generally, major characteristics of LED such as output power and wavelength of emitted light are determined by an active layer. Accordingly, a crystalline composition of the active layer is very important.
In a semiconductor device having conventional AlGaInN-based LED structure, light with only one wavelength may be emitted from the active layer, so that using fluorescent material or employing different types of LED is required to obtain various colors.
In addition, an LED package having fluorescent material in the epoxy mold shown in FIG. 3 is required to obtain white light because a light with only one wavelength is emitted from an active layer in a semiconductor device having a conventional AlGaInN-based LED structure.
An LED device 31 of FIG. 1 is mounted on an upper portion of a metal lead frame 30. Metal electrodes of the LED device are connected to the metal lead frame with a wire 32. The LED device 31 is covered with fluorescent material 33. A body 34 molded with a transparent resin is formed.
In the white light LED package, a light with a first wavelength 35 is emitted from the LED device by current supplied to the LED device. When this light excites fluorescent material, a light with a second wavelength 36 is generated by fluorescent material, and a mixed light that includes these two lights is obtained. When the colors of these two lights are complementary to each other, white light can be obtained.
For example, when a deep-blue light with 450 nm wavelength excites the fluorescent material that contains YAG, a yellow light with 590 nm wavelength can be generated. Then, by mixing these two lights, the white light LEC package may be obtained. Here, yellow wavelength tuning may be achieved by adjusting the composition of YAG fluorescent layer and adjustment of amount ratio of these two lights may be achieved by adjusting the thickness of the fluorescent layer. After that, a white light can be obtained. The white light LED package as described above can substitute a light bulb or a back light source of display device. However, while the structure and manufacturing process of the conventional white light LED package are simple, the reliability of fluorescent material is inferior to an LED device. As a result, if used for a long period, its color may fade, or its luminous efficiency may become deteriorated.
In addition, the composition adjustment of the fluorescent material and the thickness adjustment of the fluorescent layer are not so easy that the white light tuning is difficult in mass production.
To solve said problems, the present invention provides a semiconductor LED device that includes a high-power pumping layer in the device. The semiconductor LED device according to the present invention may effectively produce light with desired wavelength by the active layer absorbing the lights from the pumping layer and the absorbed light being recombined in the active layer.
In one aspect of the present invention, a semiconductor LED device comprising a substrate, a buffer layer formed on the substrate, a first n-type AlGaInN layer formed on the buffer layer; an active layer formed on the first conductive type AlGaInN layer, a second n-type AlGaInN layer formed on the active layer, a pumping layer formed on the second conductive type AlGaInN layer, a p-type AlGaInN layer formed on the pumping layer, a p-type electrode contacted with the p-type AlGaInN layer, and a n-type electrode contacted with the second n-type AlGaInN layer, wherein the pumping layer has larger bandgap than that of the active layer and emits light by recombination of electrons from the second n-type AlGaInN layer and holes from the p-type AlGaInN layer, and the active layer emits light by using light emitted from the pumping layer.
In another aspect of the present invention, a semiconductor LED device is characterized in that the active layer comprises a AlxGayInzN layer and a Alx1Gay1Inz1N layer formed on the AlxGayInzN layer with bandgap energy of the AlxGayInzN layer being smaller than bandgap energy of the Alx1Gay1Inz1N layer, and the pumping layer comprises a AlaGabIncN layer and a Ala1Gab1Inc1N layer formed on the AlaGabIncN layer with bandgap energy of the AlaGabIncN layer being smaller than bandgap energy of the Ala1Gab1Inc1N layer, wherein x+y+z=1, x1+y1+z1=1, a+b+c=1 and a1+b1+c1=1.